1. Field of the Invention
The present invention relates generally to an antenna diversity technique in a wireless terminal, and in particular, to a technique for improving transmission and reception of an HDR wireless terminal.
2. Description of the Prior Art
In a conventional wireless terminal, a transmitter shares a single antenna with a receiver. When a receiving antenna diversity technique is applied to the wireless terminal, a plurality of antennas is provided to selectively combine high-quality signals, thereby improving reception efficiency and increasing a data processing rate. FIG. 1 is schematic diagram illustrating a system for performing antenna diversity in the conventional wireless terminal. Referring to FIG. 1, the receiver Rx connected to switch SW1 detects the strength of a signal received through a specific antenna, either ANT1 or ANT2. If the signal detected through the specific antenna is above a predetermined threshold, the receiver Rx utilizes that specific antenna. If the detected signal is below the predetermined threshold, the receiver utilizes the other antenna by switching SW1 to the other antenna. After the receiver selects the antenna, the transmitter Tx utilizes the remaining antenna.
In addition, a conventional wireless terminal isolates transmission signals from reception signals through a duplexer, and performs voice and data services through a transmitter circuit and a receiver circuit. A schematic diagram of a conventional wireless terminal isolating transmission signals from reception signals through a duplexer is illustrated in FIG. 2. Referring to FIG. 2, a duplexer 200, interposed between the antenna and the transmitter Tx, isolates transmission signals from reception signals in order to perform full duplexing. That is, during transmission, the output power of the PAM (Power Amplifier Module) in the transmitter Tx (not shown) is transmitted to the antenna ANT through the duplexer 200 at maximum power. During reception, the low power RF signal is received through the antenna ANT and passed to a low noise amplifier (not shown) in the receiver Rx through the duplexer 200, to be received at maximum power. However, when transmitting transmission and reception signals at the maximum power there is a high insertion loss. Further, there is interference between the transmission and reception signals due to the incomplete isolation of the signals through the duplexer. This interference occurs because the transmission power is usually much higher than the reception power and interferes with the receiver.
A drawback with conventional wireless terminals is that when a transceiver uses a single antenna and a duplexer as a common path, a loss of the duplexer device itself and incomplete isolation between the transmitter and the receiver increase a level of the minimum detectable signal (MDS), resulting in an increase in current consumption by the wireless terminal.
Therefore, a need exists for a wireless terminal that completely isolates the transmission path from the reception path during a low data rate processing mode, and avoids using the duplexer, thus making it possible to decrease the level of the minimum detectable signal and the current consumption of the wireless telephone.